Along with rapid development in the industry of mobile communications, there is an increasingly distinct contradiction between an increasing demand for broadband wireless communication and a limited number of spectrum resources, and although Orthogonal Frequency Division Multiplexing (OFDM), Multiple Input Multiple Output (MIMO) and other technologies have been adopted in the Long Term Evolution (LTE), these cannot solve the problem of the limited number of spectrum resources thoroughly. Along with rapid development of mobile services in future, telecommunication operators will be faced with a more serious problem of the insufficient spectrum resources, and on the other hand, the spectrum use of some wireless systems is almost left unused temporally and geographically, for example, many of radio and television frequency bands have been left unused for a long time because a transmission capacity can be improved greatly by digital transmission along with evolvement of radio and television systems from analog transmission to digital transmission.
In order to solve the problem of the insufficient spectrum resources, a new radio technology, i.e., Cognitive Radio (CR), has been widely regarded. With the technology of cognitive radio, a radio system can adapt its operating parameter to its demand dependent upon its operating environment. Cognitive radio in cooperation with software radio can enable flexible use of a spectrum, have the spectrum shared and improve the efficiency of the spectrum in use.
For a typical cognitive radio system, when it is found that an authorized system is not in operation and an authorized frequency band is unused, the cognitive system makes use of the authorized frequency band and continues to detect the operating status of the authorized system in the authorized frequency band, and once it is found that the authorized system restarts its operation, a cognitive node quits the authorized frequency band and transfers to a new frequency band for further operation. Throughout this flow, the cognitive system needs to perform spectrum sensing, make a spectrum decision and transfer the spectrum. Spectrum sensing is to obtain information about a radio environment, and spectrum management is to perform corresponding management on available frequency bands according to the obtained information about the radio environment to thereby improve the efficiency of the spectrum in use; and when the authorized system starts its operation, the cognitive system needs to transfer to a new operating frequency band in order to avoid serious interference to a primary user.
Spectrum sensing is a technology in the cognitive radio system, and the cognitive node is a node in the cognitive system to perform spectrum sensing. Spectrum sensing is currently performed in two operating modes of distributed and centralized. In the distributed mode, the cognitive node in the cognitive system is separately in operation, and when it is determined that the authorized frequency band is unused, the cognitive system makes use of the authorized frequency band, and the cognitive node continues to detect the operating status of the authorized system in the frequency band, and once it is found that the authorized system restarts its operation, the cognitive system quits the frequency band; and in the centralized mode, the cognitive node in the cognitive system notifies a central node when determining that the authorized frequency band is idle, and the central node notifies the cognitive system of whether this frequency band is available, and the cognitive node notifies the central node after determining that the authorized system restarts its operation, and the central node notifies the cognitive system of whether to quit the frequency band.
The addition of the cognitive function to the wireless communication system can enhance the flexibility of the spectrum in use based upon an existing spectrum allocation policy to improve a network capacity greatly and ease the tension spectrum for telecommunication operators. An initial task of cognitive radio is to obtain information about a radio operating environment, which can be obtained through spectrum sensing, that is, a signal of a transmitter of the authorized system in a target frequency band is detected to thereby determine whether the target frequency band is available. When the target frequency band is available, the frequency band is used for cognitive radio; and when the cognitive radio system makes use of a frequency band of the authorized system, the cognitive node in the cognitive system still needs to trigger sensing periodically as to whether the authorized system restarts its operation in the current operating frequency band, and once the cognitive node finds that the authorized system reuses the frequency band, the cognitive system needs to transfer to another frequency band for further operation.
When the cognitive system makes use of a frequency band of the authorized system, spectrum sensing in the operating frequency band (in-band) is subjected to interference of the current system so that the performance of detection may not be satisfied, so a common practice is to have the cognitive radio system kept silent during spectrum sensing. The cognitive system is disabled for communication in the course of sensing during the silent period.
Existing spectrum sensing detects a signal of the authorized system in the operating frequency band (in-band) periodically in the silent period. If the sensing period is too long, after the authorized system comes into use, the cognitive node cannot find the authorized system in a timely manner, and the cognitive system continues its operation so that the authorized system is subjected to interference from the cognitive system for a long period of time, thus degrading a quality of service of the authorized system, and also the cognitive system is subjected to interference from the signal of the authorized system, thus degrading a quality of service and even seriously causing a breakdown through the network. If the sensing period is too short, then both system overhead of spectrum sensing and power consumption of a device may be increased significantly, and radio silence required by spectrum sensing may result in a waste of spectrum resources, for example, taking the sensing period of 100 ms as an example, if the silent period during spectrum sensing is 20 ms, then 20% of spectrum resources will be wasted.
In summary, currently if the sensing period is set too long, then interference between the authorized system and the cognitive system may result in a degraded quality of service and even a network breakdown; and if the sensing period is set too short, then power consumption of devices may be increased and spectrum resources will be wasted.